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Physics Physics Optics

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Friday 21 August

Optics · Cross-listed from nlin.PS

Dynamics of localized solutions in three core coupled waveguides with quasi-periodic nonlinearity

Bruno M. Miranda, Ardiley T. Avelar, Wesley B. Cardoso et al. (+1 more)

In this paper we investigate the behavior of localized solutions, specifically solitons, in a system of three coupled waveguides. The nonlinearity is modeled by a quasi-periodic modulation influencing the interaction between the waveguides. We analyze the evolution of the soliton profiles and their dynamics under varying modulation parameters, highlighting distinct behaviors such as attraction and repulsion among solitons. Our findings reveal that the system exhibits complex behaviors, depending on the interplay between the quasi-periodic modulation and the waveguide parameters. The study contributes to understanding the impact of quasi-periodic nonlinearity on soliton dynamics in coupled waveguide systems, laying the groundwork for potential applications in nonlinear optics and photonic devices.
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All authors Bruno M. Miranda, Ardiley T. Avelar, Wesley B. Cardoso, Dionisio Bazeia

Optics

Oblique Bragg-Doppler scattering at relativistic grating created by backward Raman amplification in hydrogen

Wenhong Lai, Jiapeng Huang, Haozhe Guo et al. (+1 more)

We report the first observation of relativistic "Bragg-Doppler" reflection, which occurs when a light beam is incident on a fine-period phase grating moving at close to the speed of light. The grating is created in hydrogen-filled hollow-core fibre by seeded backward stimulated Raman scattering, which creates an intense coherence wave of molecular vibrations at 125 THz, with wavelength 299 nm, moving at ~c/8. When this grating is obliquely probed at a generalized Bragg angle, a reflected beam emerges, Doppler-shifted by 125 THz. The effect is also uni-directional, as phase-matching is strongly violated when the probe beam is reversed, so may be viewed as an ultra-high frequency Bragg-cell frequency-shifter. The wide transparency window of hydrogen allows frequency shifting of radiation from the visible to the vacuum UV, simply by tuning the incident angle. The results open up new opportunities for spatio-temporal studies of coherence wave dynamics, frequency conversion in difficult-to-access spectral regions such as the deep and vacuum UV, and quantum-state-preserving frequency conversion of single photons.
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All authors Wenhong Lai, Jiapeng Huang, Haozhe Guo, Philip St.J. Russell

Optics

A Fourier Neural Operator for Accelerated Discretization-Invariant Solutions of the Radiative Transfer Equation

Daniel Carne

The radiative transfer equation (RTE) governs thermal radiation in participating media, which is critical to modeling combustion, atmospheric, high-temperature, and radiative thermal management applications. However, due to the inherently high-dimensional nature of radiative transfer, numerical solutions to the RTE induce significant computational cost. This work develops a Fourier neural operator (FNO) as a fast, discretization-invariant, surrogate model for predicting the absorbed heat flux field in participating media. A dataset is generated on a benchmark 2-dimensional problem modeling thermal surface emission into a participating medium with spatially varying properties using Monte Carlo simulations. The FNO is trained to learn the solution operator, mapping the input property fields and geometry to the resulting heat flux field. The trained FNO provides up to 26-times computational acceleration compared to Monte Carlo simulation at equivalent error. Furthermore, as the FNO learns the solution operator and not an image-to-image mapping, the trained FNO accurately generalizes to various spatial discretizations, including those not seen in the training dataset. A spectral analysis of the spatial frequencies present in the heat flux prediction demonstrates the FNO's ability to suppress the high-frequency noise present in the training dataset, while preserving the physically meaningful low-mid frequency spectrum. These results demonstrate the Fourier neural operator surrogate model can provide accurate, computationally efficient, and discretization-invariant predictions for radiative transfer in a participating medium. By learning the underlying solution operator, this approach moves toward the development of surrogate models for radiative transfer capable of generalizing across a broad range of geometries, discretizations, and boundary conditions.
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Optics

Neuromorphic Infrared Fibre-Optic Event-Based Sensing with Fast and Efficient Photonic-Electronic Spiking Neurons

Dylan Black, Giovanni Donati, Joshua Robertson et al. (+5 more)

Current photonic technologies for remote sensing require the capture of large amounts of data, suffering as a result from high energy consumption, excessive data redundancy and storage, and costly data processing requirements, limiting their ability for direct and efficient edge-processing for rapid decision making and alarm triggering. In contrast, biological sensing systems, given their event-driven nature and in-sensor processing capabilities offer energy-efficient and practical alternatives. In this work, we draw direct inspiration from the neural spiking in biological sensory systems, to propose a novel neuromorphic event-based photonic technology permitting the remote sensing of environmental events-of-interest efficiently, at high speeds and across a wide dynamic frequency range. Our approach combines widely-deployed fibre-optic telecommunication links and photo-detecting resonant tunnelling diodes (pRTD) acting as light-triggered spiking neurons. We demonstrate that this new neuromorphic photonic sensing approach allows the remote detection of different types of environmental events, including temperature variations, strain-induced motion, audio and air turbulence, with high temporal resolution (encoding them with fast nanosecond-rate neural-like spikes). These results pave the way for novel light-enabled neuromorphic remote infrared fibre-optic sensing networks that are fast, efficient, event-driven, scalable, permit direct processing at-the-edge, and offer practical alternatives to current data-intensive approaches for photonic remote sensing.
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All authors Dylan Black, Giovanni Donati, Joshua Robertson, Qusay Raghib Ali Al-Taai, José Figueiredo, Edward Wasige, Bruno Romeira, Antonio Hurtado

Optics · Cross-listed from cond-mat.mes-hall

Electric-Field-Induced Second Harmonic Generation at a Reconfigurable LaAlO$_3$/SrTiO$_3$ Nanojunction

Pubudu Wijesinghe, Melanie Dieterlen, Kyoungjun Lee et al. (+5 more)

Electrically tunable nonlinear optical responses at the nanoscale remain challenging to achieve because conventional nonlinear materials lack the combination of large susceptibility, nanoscale confinement, and in situ reconfigurability. Here we report electric-field-induced second harmonic (EFISH) generation from a nanoscale tunnel junction defined by conductive atomic force microscope lithography at the LaAlO$_3$/SrTiO$_3$ interface. A conducting channel written at the interface is interrupted by a nanoscale insulating gap, across which applied DC bias produces local electric fields exceeding $10^7$ V/m. The SHG signal is spatially localized at the junction, exhibits a quadratic bias dependence described by $I(2\omega) \propto |\chi^{(2)}_\mathrm{0} + \chi^{(3)} E_\mathrm{DC}|^2$ with no hysteresis, a modulation depth exceeding 380% at $|V_\mathrm{DC}| = 1$ V, and shows a two-lobed input-polarization pattern aligned with the junction axis, consistent with EFISH from a centrosymmetric host. Calibration against a BBO reference crystal gives $|\chi^{(3)}| \approx 1\times10^{-19}$ m$^2$/V$^2$ at 6 K. These results establish cAFM-written oxide nanojunctions as a reconfigurable platform for nanoscale nonlinear optics in which the junction geometry sets the symmetry of the response and the large field-induced $\chi^{(2)}$ of SrTiO$_3$ provides the optical nonlinearity. Because the nonlinearity is both generated and read out within the same nanoscale gap, the junction operates simultaneously as a subwavelength source and a near-field detector of optical nonlinearity.
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All authors Pubudu Wijesinghe, Melanie Dieterlen, Kyoungjun Lee, Ahmed Omran, Aswini Ramankutty, Chang-Beom Eom, Patrick Irvin, Jeremy Levy

Optics · Cross-listed from quant-ph

Minimization of micromotion for nanoparticles in a Paul trap

Jamie Morley, Jean Paul Louys Sansó, Dmitry Bykov et al. (+2 more)

When a charged particle in a Paul trap is displaced from the node of the AC trapping field, excess micromotion arises as an undesired effect. Excess micromotion heats the particle, limits the precision with which the particle can be localised, and acts as a decoherence channel in quantum mechanical experiments. However, thus far there is no standard procedure for micromotion compensation with mesoscopic particles. Here, we experimentally demonstrate three different methods for minimizing the micromotion of a nanoparticle in a linear Paul trap along three axes. The most precise method allows us to nullify the stray field to within 2.9 V/m, which is comparable to reported values in trapped-ion experiments.
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All authors Jamie Morley, Jean Paul Louys Sansó, Dmitry Bykov, Simon Baier, Tracy Northup

Optics

Artificial Anisotropy Induced Bound States in the Continuum for Integrated Photonic Waveguide

Jinzhao Wang, Kunrun Lu, Yuanlin Li et al. (+9 more)

Bound states in the continuum (BICs) enable counterintuitive light confinement without radiation loss, providing a powerful foundation for integrated photonic waveguides. However, existing BIC waveguides are predominantly realized through geometry-dependent designs, where the BIC condition is restricted to narrowly defined structural parameters, limiting design flexibility and practical applicability. Artificial optical anisotropy is introduced as a new design paradigm for BIC waveguides. Implemented using subwavelength-grating (SWG) metamaterials, continuously tailorable anisotropy provides an independent degree of freedom for deterministically reshaping the radiative continuum, enabling flexible formation and systematic control of BIC waveguides over a broad design space. Anisotropy-engineered symmetry breaking further enables controllable asymmetric radiation and precisely tailored field leakage. This paradigm transforms BIC waveguides from geometry-constrained structures into an anisotropy-engineered platform, establishing a general framework for programmable radiation engineering and next-generation integrated photonic devices.
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All authors Jinzhao Wang, Kunrun Lu, Yuanlin Li, Weiming Yao, Yang Feng, Yidi Cao, Wei Liu, Feng He, Jianan Duan, Yi Zou, Yongkang Dong, Xiaochuan Xu

Optics

Direction-Selective Wave Freezing and Amplification at a Hyperbolic Time Interface

Zhao Wang, Ai Gang, Xinghong Zhu et al. (+3 more)

Hyperbolic media are well known for converting high k-components that are evanescent in conventional dielectrics into propagating bulk waves through their open equifrequency contours. Here, we reveal a complementary temporal effect: after a sudden transition into an effectively nondispersive hyperbolic state, conservation of the full wavevector causes the indefinite dispersion to partition momentum space into real-, zero-, and purely imaginary-frequency regimes. Consequently, p-polarized waves undergo conventional temporal scattering, critical magnetic-field freezing, or exponential growth and decay, depending solely on their conserved wavevector direction, whereas s-polarized waves remain in the real-frequency regime. A second temporal boundary releases the frozen or amplified fields into propagating waves at original frequency. Analytical temporal boundary theory, k-space pulse reconstruction, and finite-difference time-domain simulations corroborate these dynamics. These results establish hyperbolic temporal boundaries as a compact route to direction-selective imaginary frequency dynamics and wave amplification without Floquet periodicity.
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All authors Zhao Wang, Ai Gang, Xinghong Zhu, Hongru Ma, Wen Xiao, Huanyang Chen

Optics

High-Resolution Speckle-based Single-Pixel Imaging using Silicon Photonic Non-Redundant Optical Phased Array

Keita Hirashima, Taichiro Fukui, Kento Komatsu et al. (+3 more)

Optical phased arrays (OPAs) are promising wavefront controlling devices for imaging applications due to their compact and high-speed nature. However, conventional periodic OPAs have a limited spatial resolution, which scales only linearly with the number of optical antennas $N$. Here, we experimentally demonstrate high-resolution imaging using a non-redundant OPA (NR-OPA). Due to the non-redundant antenna layout of NR-OPA based on the Costas array, the resolution scales quadratically with $N$. Combined with the speckle-based single-pixel imaging (SSPI) scheme, which avoids the need for precise phase calibration, we experimentally achieve a large number of resolvable imaging points exceeding 10,000 using a silicon photonic NR-OPA chip with only $N=127$ without sweeping the wavelength. The demonstrated scheme provides a promising route toward mega-pixel imaging by a compact OPA chip with reduced number of phase shifters.
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All authors Keita Hirashima, Taichiro Fukui, Kento Komatsu, Chun Ren, Yoshiaki Nakano, Takuo Tanemura

Optics

Differentiable high-fidelity vectorial propagator

Dohyun Kim and Jonghwa Shin

The numerical accuracy and computational efficiency of free-space field propagation directly determine what physics can be predicted and what devices can be designed, from nanophotonic metasurfaces to optically addressed quantum processors. Existing methods face a fundamental accuracy-speed trade-off, which is further compounded in the vectorial regime, where major formalisms remain fragmented with no unified computational framework. Here we address both challenges: a theory that unifies the vectorial diffraction framework, and an algorithm that resolves the accuracy-speed trade-off, each reinforcing the other. We prove that all major vectorial diffraction formalisms and vector-potential seeding methods arise from a single surface equivalence principle and reduce, without approximation, to a finite sequence of scalar angular-spectrum operations. Any advance in scalar propagation can therefore be exploited across the entire vectorial ecosystem. The error-compensating angular spectrum method (E-ASM) serves as a fast and accurate scalar solver, delivering peak signal-to-noise-ratio gains exceeding 60 dB over the state-of-the-art band-extended angular spectrum method at order-of-magnitude faster speed, with a freely configurable observation window. Their combination, implemented in a GPU-accelerated, fully differentiable form, turns rigorous vectorial field computation, previously prohibitive for higher-order beams over macroscopic distances, into a practical, inverse-design-ready tool. We demonstrate the framework on optically addressed local qubit gates and on vectorial Hermite-Gaussian and Laguerre-Gaussian beam propagation, resolving field structures inaccessible to scalar or approximate vectorial methods.
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Optics

Spectral Anisotropy in Transition Radiation from Biaxial Media

Sven Ebel, Bibi Mary Francis, Min Seok Jang et al. (+4 more)

In anisotropic optical media, the electromagnetic response depends on the orientation of the optical field relative to the material's principal dielectric axes. While this direction dependence is well understood in conventional optics, it should also influence light-generation processes driven by free electrons. Here, we experimentally observe spectrally anisotropic transition radiation from biaxial van der Waals crystals. Using cathodoluminescence spectroscopy on germanium sulphide (GeS) and molybdenum oxydichloride (MoOCl$_2$) crystals, we show that the transition-radiation spectra differ along the principal in-plane optical axes. To describe this spectral anisotropy, we develop a thin-film transition-radiation model that reproduces the experimental observations. Our results demonstrate that transition radiation is a sensitive probe of the axis-dependent dielectric response of biaxial optical media and suggest that optical anisotropy can provide an additional degree of freedom for free electron-driven spectroscopy, radiation sources, and transition-radiation-based diagnostics.
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All authors Sven Ebel, Bibi Mary Francis, Min Seok Jang, Brian D. Gerardot, N. Asger Mortensen, Mauro Brotons-Gisbert, Sergii Morozov

Optics · Cross-listed from cs.AI

VortexChat: An agentic framework for autonomous multi-objective integrated photonic design

Faqian Chong, Yulun Wu, Shilong Li et al. (+3 more)

The advancement of modern integrated photonics is frequently bottlenecked by device design workflows that rely heavily on manual simulation and expert intuition. While inverse design offers an alternative, it remains constrained by expert supervision and a lack of end-to-end automation. To address these issues, we present VortexChat, an agentic framework for the autonomous, end-to-end inverse design of integrated photonic devices directly from natural language specifications. VortexChat couples a large language model (LLM) decision agent with topology generation, gradient-based refinement, and full-wave electromagnetic simulation. This closed-loop architecture enables the system to iteratively decompose design objectives, orchestrate computational tools, and update strategies based on feedback with minimal human intervention. Constrained by the absolute metrics of the Vortex100 Benchmark, VortexChat autonomously generates devices that strictly meet all predefined performance thresholds without any human-in-the-loop. As an experimental demonstration, we fabricated a broadband terahertz perfect vortex beam multiplexer, autonomously designed by VortexChat, with measurements confirming high-efficiency operation, high mode purity and low inter-channel crosstalk in agreement with full-wave simulations. These results demonstrate that an LLM agent can assume key aspects of expert decision-making in photonic inverse design while maintaining physical fidelity and fabrication feasibility, providing a scalable route towards autonomous design of complex integrated photonic systems.
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All authors Faqian Chong, Yulun Wu, Shilong Li, Andrew Forbes, Hongsheng Chen, Song Han

Optics

Gas Beam Dump and Power Meter for High Energy Lasers

Harsha Rajesh, Sida Cao, Ke Ou et al. (+3 more)

Gaseous optics exhibit substantially higher laser-induced-damage thresholds than solid materials, enabling high-intensity operation without permanent degradation. In this Letter, we describe a gas-based beam dump and power meter that exploits the strong absorption of ozone in the Hartley band (200-320 nm). We develop and experimentally validate a model for ozone absorption that predicts the propagation length required for complete energy deposition and the resulting gas temperature rise. By calibrating the temperature rise against incident pulse energy, we demonstrate accurate millijoule-scale pulse energy measurements with an all-gas absorber. These results establish gas-phase absorbers as a scalable, debris-free platform for high-damage-threshold beam dumps and energy diagnostics for high-fluence lasers.
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All authors Harsha Rajesh, Sida Cao, Ke Ou, Devdigvijay Singh, Pierre Michel, Matthew R. Edwards

Thursday 20 August

Optics · Cross-listed from quant-ph

Atmospheric Turbulence-Aware Optimization of Generalized Kennedy Receivers for Coherent-State BPSK Quantum Communication

Md Ashraf Hossain Ifty and Rahul Bhadani

We investigate generalized Kennedy receivers for coherent-state BPSK communication over turbulent free-space optical channels. An ergodic mutual-information framework is developed to jointly optimize the receiver displacement and input prior probabilities under Gamma–Gamma fading.
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Optics

Sidewall-Poled Nanophotonic Lithium Niobate with Bidirectional Characterization

Aditya Tripathi, Michael S. Bullock, Parash Thapalia et al. (+10 more)

Accurate characterization of integrated nonlinear photonic devices is often limited by unknown facet-coupling losses and fabrication-induced non-uniformities, leading to systematic over- or underestimation of the intrinsic on-chip performance. Here, we present and demonstrate a unified bidirectional characterization framework that exploits nonlinear interactions under forward and backward propagation to independently extract facet-specific coupling efficiencies, intrinsic nonlinear conversion efficiency, and the longitudinal quasi-phase-matching profile using only classical power measurements. We experimentally validate the method using sidewall-poled thin-film lithium niobate waveguides, obtaining a normalized second-harmonic generation efficiency of $(1850 \pm 20)~\%\mathrm{W}^{-1}$ while simultaneously demonstrating broadband non-degenerate optical parametric amplification and parametric generation spanning more than $10~\mathrm{THz}$. Our framework is non-destructive, relies solely on classical power measurements, requires neither time-intensive microscopy nor calibrated internal references, and is compatible with wafer-scale testing, providing a general route to rigorous benchmarking and high-throughput characterization of photonic devices across material platforms.
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All authors Aditya Tripathi, Michael S. Bullock, Parash Thapalia, Pooja Kulkarni, Jaber Balalhabashi, Robert Kwolek, Shiva Behzadfar, Kazuki Hirota, Shion Eto, Rintaro Tsuchida, Liam Beaudoin, Sasan Fathpour, Rajveer Nehra

Optics

Impact of Plasmonic Modes and Thermophysical Properties on the Double-Pulse Structuring of Highly-Ordered LIPSS for Biosensing Applications

G.D. Tsibidis, F. Fraggelakis, P. Lingos et al. (+5 more)

The fabrication of highly ordered laser-induced periodic surface structures (LIPSS) on thin metallic films is dictated, predomaninatly, by a synergy of periodic electromagnetic energy deposition and complex fluid dynamics. In this work, we present a combined experimental and theoretical study on the formation of ultra-regular LIPSS on 32-nm-thick Au films using a double-pulse femtosecond laser scheme. We demonstrate that for thin films, the excitation of coupled Surface Plasmon Polaritons (SPPs) at both interfaces dictates the initial energy distribution. On the othe hand, the final morphology is greatly influenced by hydrodynamical processes. Interestingly, due to the low electron-phonon coupling of Au and the high thermal confinement of the thin film, single-pulse irradiation leads to uncontrolled hydrodynamic instabilities a non uniform topographies. Thus, we demonstrate that a double-pulse approach with an optimized interpulse delay ({\Delta}{\tau}=1.2 ns) effectively controls the melt duration and viscosity, suppressing complex fluid motion and promoting the growth of highly ordered arrays. These structures support narrow surface lattice resonances (SLRs) suitable for high-sensitivity plasmonic biosensing.
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All authors G.D. Tsibidis, F. Fraggelakis, P. Lingos, E. Cusworth, V.G. Kravets, A.N. Grigorenko, A.V. Kabashin, E. Stratakis

Optics

Beat-spectrum design for 100-km-range optical correlation-domain reflectometry with localized 15-cm resolution

Takaki Kiyozumi, Yuta Higa, Soshi Yoshida et al. (+4 more)

Conventional optical correlation-domain reflectometry (OCDR) based on sinusoidal frequency modulation exhibits a coupling between measurement range and spatial resolution because both are governed by the modulation frequency. Here, we formulate OCDR for arbitrary periodic frequency modulation and relate the modulation waveform to the resulting beat spectrum. By expressing the instantaneous optical frequency as a Fourier series, the beat spectrum is written as successive convolutions of the spectral contributions from the harmonic components. This formulation relates the harmonic composition of the modulation waveform to the spatial response. Periodic pseudo-random modulation (PPRM) was used to test this relation experimentally. We first measured the full-length reflectivity distribution along an approximately 100-km fiber using sinusoidal modulation and then performed PPRM-based random access interrogation near the fiber end. In the local measurement, two closely spaced reflection points were resolved with a correlation-peak width of approximately 15 cm. These results show that beat-spectrum design can reduce the range-resolution coupling of conventional sinusoidal-modulation OCDR and combine long-range surveying with localized high-resolution interrogation.
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All authors Takaki Kiyozumi, Yuta Higa, Soshi Yoshida, Keisuke Motoda, Sze Yun Set, Shinji Yamashita, Yosuke Mizuno

Optics · Cross-listed from physics.chem-ph

Real-time ESR tracking for sub-micron 3D magnetic mapping with VB- quantum sensors in hexagonal boron nitride

Jefferson A. O. Galindo, Edwin D. C. Sanchez, Cecília L. A. V. Campos et al. (+6 more)

The discovery of spin-dependent luminescent properties of negatively charged boron-vacancy centers ($V^-_B$) in hexagonal boron nitride (hBN) enabled a new platform for quantum sensing with van der Waals materials. Particularly, the possibility of performing optically detected magnetic resonance (ODMR) for determining the electron spin resonance (ESR) frequencies of hBN color centers became a strong tool for quantum sensing of magnetic fields with submicrometric resolution. However, due to low ODMR contrast, current techniques proposed for mapping DC magnetic fields require hours of integration to obtain a magnetic image of a micron-sized region. In this work, we report the implementation of a frequency-tracking approach for real-time monitoring of ESR frequencies of localized $V^-_B$ centers in hBN. With this technique, magnetic field monitoring was used to map the field pattern generated by a micron-sized conical magnetic tip in only a few minutes. By controlling the magnetic sample's position relative to the quantum sensor, three-dimensional magnetic mapping of the field was achieved with diffraction-limited resolution and shot-noise-limited sensitivity of 54 $\mu$T$/\sqrt{\text{Hz}}$. Magnetic field gradients of 3.6 $\pm$ 0.2 $\mu$T/nm were measured with our system, in which a maximum detected field rate of 6 mT/s was achieved. The results of this study establish spin resonance frequency-tracking as a viable technique and fast method for minute-scale magnetic imaging, reducing acquisition times by at least one order of magnitude if compared to conventional techniques.
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All authors Jefferson A. O. Galindo, Edwin D. C. Sanchez, Cecília L. A. V. Campos, Allison R. Pessoa, Hugo A. D. Correia, José D. M. de Lima, Klaus Krambrock, Leonardo de S. Menezes, Anderson M. Amaral

Optics

Computational Methods of Wave Propagation for Semiclassical Models of High Harmonic Generation in Bulk Solids

Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes et al. (+1 more)

We present a theoretical framework for self consistent treatment of nonlinear light-matter interactions in the ultra-fast strong-field regime based on numerical solution of Maxwell's equations and semiconductor Bloch equations. This framework is shown to describe high-order harmonic generation and propagation in bulk semiconductors, investigating differences in reflected and transmitted harmonic spectra due to propagation effects. We show that the propagation of the combined field of the driving laser pulse and generated harmonics in a bulk semiconductor significantly modifies the harmonic spectra, affecting interpretation of experimental results relating the transmitted harmonic spectra to the underlying electronic structure of the material. This model allows the self-consistent description of strong-field light-matter interactions in the non-perturbative regime, opening the way to explore the transition between fully classical and quantum regimes of interaction, tunneling and multiphoton regimes of material ionization, and perturbative and non-perturbative regimes of harmonic generation in bulk materials.
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All authors Ava N. Hejazi, Nicholas Karpowicz, Gregory D. Scholes, Julia M. Mikhailova

Optics

Point Spread Function Engineering Using Implicit Neural Representations

Suet Ying Chan, Mitchell Gilmore, Qilin Deng et al. (+4 more)

Point spread function (PSF) engineering through pupil plane modulation is a technique used in microscopy to achieve specific imaging properties, such as depth encoding or extended depth of field. Existing PSF design methods often rely on extensive domain knowledge and task-specific basis functions, making it difficult to generalize across different applications. We treat the PSF engineering task as a phase retrieval problem and propose a neural field pupil design method that optimizes a phase profile for any arbitrary, user-defined 3D PSF distribution. This provides a flexible framework for 3D PSF engineering for various applications with implicit regularization that proves robust to initialization compared to pixel-wise optimization methods
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All authors Suet Ying Chan, Mitchell Gilmore, Qilin Deng, Guorong Hu, Joseph Greene, Ruipeng Guo, Lei Tian

Optics

Intensity-based scattering correction enables in vivo two-photon imaging beyond 1 mm

Yucheng Li, Renzhi He and Yi Xue

Optical imaging of the deep brain with subcellular resolution is essential for neuroscience, but noninvasive imaging beyond the cortex, through scattering white matter and into the hippocampus, has generally required three-photon microscopy at longer excitation wavelengths. Here, we introduce deep-learning-enhanced Fourier-domain intensity coupling for scattering correction (DeepFOCUS), an intensity-based two-photon approach that uses deep learning to compute intensity-modulation masks for real-time modulation of excitation light during image acquisition. Unlike deep-learning-based image restoration, this method directly improves image formation by computing intensity-modulation masks that shape the excitation light in real time, with each mask experimentally validated by the acquired fluorescence signal to avoid hallucination artifacts. Using 1035 nm excitation, we achieved in vivo two-photon imaging beyond 1 mm depth in the intact mouse brain, resolving YFP-labeled neurons and FITC-labeled blood vessels through the entire cortex and white matter down to the CA1 region of the hippocampus. DeepFOCUS extends two-photon imaging to depths previously accessible mainly with three-photon microscopy and could enable broader adoption of hippocampal imaging by upgrading existing two-photon systems.
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Optics · Cross-listed from cond-mat.mes-hall

Floquet Theory for Light-Driven Rotation of Dipolar and Multipolar Particles

Amane Takano, Minoru Kanega and Masahiro Sato

Nano- or micro-particle rotation driven by light has been well known in the fields of optical manipulation and optical physics since the end of the last century. It is viewed as a sort of angular-momentum transfer from light to material, but its microscopic analysis based on the Hamiltonian or the equation of motion has been less developed. We model this rotation with a simple setup of an electrically dipolar or multipolar particle irradiated by circularly polarized laser and comprehensively analyze the Langevin-type equation of motion by using the Floquet theory for dissipative classical systems and the mode separation method. Furthermore, we numerically compute the time evolution of the particle. As a result, we accurately estimate the dependence of the laser-frequency, laser-intensity, particle mass, temperature, and friction (dissipation) on the laser-driven rotation. We determine the “nonequilibrium phase diagram” of the laser-driven rotation in a broad parameter regime, which consists of three regimes: the rotation frequency $\Omega\propto\omega^{-1}$, $\Omega\propto\omega^{-3}$, or $\Omega=\omega$ ($\omega$ is the laser frequency). Comparing our theoretical result with some experiments, we show that the result of the overdamped Langevin equation is qualitatively consistent with the experiments.
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Optics

Wavefront shaping of terahertz radiation using two-color flying-focus pulses with time-dependent focal velocities

A.L. Elliott, H. Markland, K.G. Miller et al. (+3 more)

Properly phased two-color laser pulses drive photoionization currents that emit broadband THz radiation. With a conventional two-color pulse, the ionization front travels at a nearly constant superluminal velocity, generating THz radiation with conical wavefronts at a Cherenkov-like angle. Here we show that the dynamic intensity peak of a two-color ultrashort flying-focus pulse can be used to control the shape of the THz wavefronts. Simulations demonstrate that non-uniform motion of the intensity peak and the ionization front it drives result in a time-dependent emission angle that determines the wavefront shape. A decelerating intensity peak, in particular, enables the generation of THz radiation with parabolic wavefronts that are well suited for collection and focusing.
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All authors A.L. Elliott, H. Markland, K.G. Miller, S.W. Jolly, J.J. Pigeon, J.P. Palastro

Optics

Symmetry-guided modal control in elliptical femtosecond-laser-written photonic waveguides

Tadas Paulauskas, Ubaid Ur Rehman, Eimantas Dermauskas et al. (+1 more)

Few-mode photonic circuits can increase functionality without multiplying waveguide paths, but bends and fabrication errors can mix their transverse modes. We investigate a strategy in which waveguide confinement and perturbation parity are engineered together in vertically elliptical, femtosecond-laser-written glass waveguides. The intended modal basis comprises the even $1S$ mode and the vertically odd $2P_y$ mode. No window-converged $2P_x$ state is resolved for a lower-confinement (LC) design, whereas a higher-confinement (HC) design guides $2P_x$, which must therefore be isolated by symmetry. In scalar beam-propagation calculations, the $1S$-$2P_y$ propagation-constant splitting predicts the optimized periods of a vertically modulated coherent modal splitter to within $1.0\%$. Horizontal S-bends remain parity-mismatched for $1S \leftrightarrow 2P_y$ coupling, while the symmetry-allowed HC $1S \rightarrow 2P_x$ transfer reaches only $0.6\%$ at the largest displacement. At a displacement of $150~\mu\mathrm{m}$, the HC design retains approximately the same $2P_y$ power as the LC design retains at $40~\mu\mathrm{m}$. Thermal and stochastic writing-error calculations reveal the resulting trade-off: stronger confinement improves modal-power retention, but writing jitter that breaks $x$-parity can populate the guided $2P_x$ mode. These results demonstrate how modal-basis engineering can shift part of the crosstalk-control burden from the trajectory to waveguide symmetry, supporting joint path–mode degrees of freedom in quantum photonic applications.
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All authors Tadas Paulauskas, Ubaid Ur Rehman, Eimantas Dermauskas, Valdemar Stankevic

Optics

Geometric Control of Cat States in High Harmonic Generation

Arti Gaharwar, Rocío Borrego-Varillas, Marcelo F. Ciappina et al. (+6 more)

High-harmonic generation (HHG) provides a powerful platform for exploring the interaction between intense laser fields and matter on ultrafast timescales. Beyond its conventional description in terms of emitted radiation and electron dynamics, a fully quantum treatment of HHG reveals that the nonlinear light-matter interaction can modify the quantum state of the driving field itself, establishing correlations between the fundamental and harmonic modes. This perspective opens new possibilities for using HHG as a tool to engineer and control nonclassical states of light. In this work, we investigate the geometric properties of optical Schroedinger cat states generated in HHG via conditioning and post-selection. By analyzing the coherent-state displacements induced by different structured driving fields, we characterize the resulting phase-space evolution and the associated geometric phases of the generated quantum states. Particular emphasis is placed on how the polarization and spatial-mode structure of the driving light influence the geometry and evolution of displaced coherent states. Our results demonstrate that structured light offers a versatile means of controlling the geometric dynamics of HHG-generated cat states across the parameter space. Furthermore, we discuss the prospects for realizing genuinely topological optical cat states by exploiting more complex structured light configurations.
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All authors Arti Gaharwar, Rocío Borrego-Varillas, Marcelo F. Ciappina, Anna G. Ciriolo, Javier Rivera-Dean, Philipp Stammer, Paraskevas Tzallas, Emilio Pisanty, Maciej Lewenstein

Optics · Cross-listed from physics.app-ph

Mid-infrared distributed-feedback lasing from black phosphorus under nanosecond excitation

Julien Brodeur, Laure Sène and Stéphane Kéna-Cohen

Mid-infrared (MIR) light sources compatible with silicon photonics are highly desirable for environmental sensing and free-space optical communications. Conventional GaSb-based quantum-well and interband-cascade lasers, however, rely on complex epitaxial heterostructures, complicating their integration with silicon photonic platforms. Here, we demonstrate a room-temperature MIR surface-emitting distributed-feedback (DFB) laser using black phosphorus (b-P) as the active gain medium. By deterministically integrating exfoliated b-P flakes onto lithographically patterned SiO$_2$ gratings, we obtain narrowband emission with a full width at half maximum below 3 nm under 1064 nm optical excitation. The lasing wavelength is tunable from 3.79 to 4.05$~\mu\text{m}$ through the b-P flake thickness, covering a technologically important region of the mid-infrared. Room-temperature thresholds as low as $(0.25 \pm 0.07)\ \text{mJ/cm}^2$ are achieved under nanosecond excitation. Upon cooling to 110 K, the threshold decreases tenfold to $(0.015 \pm 0.005)\ \text{mJ/cm}^2$. These results establish planar b-P DFB cavities as a promising platform for heterogeneously integrated MIR lasers based on van der Waals semiconductors.
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Optics · Cross-listed from physics.acc-ph

Mutually phase-stable tunable attosecond soft X-ray attosecond pulses from a free-electron laser

River Robles, Kurtis Borne, Mathew Britton et al. (+16 more)

We demonstrate the production of mutually phase-stable attosecond X-ray pulse pairs with tunable relative time delays and phases in a cascaded X-ray free-electron laser. We showcase the method in an experiment at the LCLS-II, in which a shaped electron beam is used in a split undulator configuration to generate the two attosecond pulses. We achieve mutual phase stability by reusing microbunching generated in the first undulator in order to seed the FEL process in the second at a detuned frequency. We measure controllable temporal delays between the two pulses directly in the time domain using angular streaking of photoelectrons, with a step size of 250 attoseconds. We then show that the behavior of the X-ray spectrum is consistent with phase stability between the two pulses, with a relative phase that can be easily tuned using inter-undulator phase shifters. This method is particularly well-suited to few to ten eV energy separations and sub to few femtosecond time delays, which are ideal for experiments in the soft X-ray regime for pushing the limits of our models for molecular dynamics and exerting direct coherent control over quantum systems.
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All authors River Robles, Kurtis Borne, Mathew Britton, David Cesar, Paris Franz, Veronica Guo, Gabriel Just, Kirk A. Larsen, Randy Lemons, Vyacheslav Leshchenko, Xiang Li, Ming-Fu Lin, Razib Obaid, Nicholas Sudar, Jun Wang, Zhen Zhang, James Cryan, Taran Driver, Agostino Marinelli

Optics · Cross-listed from quant-ph

Wide-field mid- to long-wave infrared imaging with undetected photons

Vladimir Kornienko, Nathan Gemmell, Caiyi Liu et al. (+3 more)

Quantum imaging with undetected photons (QIUP) allows an object to be probed at mid-infrared frequencies by only measuring interference in the visible range, thus leveraging silicon camera technology. We show that non-collinear phase-matching in a silver thiogallate (AgGaS$_2$) crystal enables wide-field QIUP in the wavelength range of 6-10 $\mu$m (1670-1000 cm$^{-1}$). A combination of coherent detection and infrared photons being “undetected” enables imaging at ${\sim}$100 times better than the background-limited infrared photodetection (BLIP) limit. At 8 $\mu$m, our images have over 8000 $\pm$ 100 resolvable elements with a 297 $\pm$ 5 $\mu$m resolution, and 10 s acquisition time. Our results pave the way to fast, background-noise-free, room-temperature, spectrally-selective mid-infrared imaging.
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All authors Vladimir Kornienko, Nathan Gemmell, Caiyi Liu, Asteria Chen, Chris Phillips, Rupert Oulton

Optics · Cross-listed from physics.comp-ph

Resonant state expansion for acoustic resonators. Part II. Scattering problem

Egor Domoratskii, Vladimir Igoshin, Nikolay Solodovchenko et al. (+4 more)

We develop a resonant-state expansion formulation for acoustic scattering by individual resonators. The scattered pressure and particle-velocity fields are expanded over the resonant states of the system, with excitation amplitudes determined by overlap integrals between the incident field and the resonant states over the resonator volume. Using the acoustic energy flux, we derive expressions for the extinction, scattering, and absorption cross-sections and show that the extinction spectrum can be resolved into contributions from individual resonant states. The formulation is first validated for a homogeneous two-dimensional cylinder, where it reproduces the analytical Mie-theory solution. We then consider a sectorally perturbed cylinder with coupled azimuthal modes and demonstrate agreement with finite-element simulations. Finally, we combine the eigenvalue and scattering formulations for a material-programmed hard-wall annular metaatom and reproduce its scattering spectra and near fields. The developed framework provides a physically transparent modal approach to acoustic scattering by open resonators with reduced symmetry and spatially structured material parameters.
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All authors Egor Domoratskii, Vladimir Igoshin, Nikolay Solodovchenko, Mingzhao Song, Yong Li, Mihail Petrov, Andrey Bogdanov

Optics · Cross-listed from physics.comp-ph

Resonant state expansion for acoustic resonators. Part I. Eigenvalue problem

Egor Domoratskii, Vladimir Igoshin, Nikolay Solodovchenko et al. (+4 more)

Resonant-state expansion (RSE) is a powerful modal framework for the perturbative analysis of open resonant systems, providing direct access to complex eigenfrequencies and eigenmodes. While RSE is well developed in electromagnetism, a comparably systematic formulation for acoustics remains less established. Here, we develop a general Green-function-based formalism for acoustic RSE and illustrate it for a class of two-dimensional acoustic resonators. Using the resonant states of an analytically solvable cylindrical reference system as a basis, we derive explicit perturbation matrix elements for uniform, radial, and sectoral variations of density and compressibility, representing homogeneous tuning, graded profiles, and symmetry-induced modal coupling. The resulting complex eigenfrequencies and eigenmodes are validated against exact analytical solutions and finite-element simulations, showing excellent quantitative agreement. The framework provides a systematic and physically transparent approach for analyzing perturbed open acoustic resonators and establishes a basis for resonant-state methods in acoustic metamaterials and non-Hermitian acoustics.
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All authors Egor Domoratskii, Vladimir Igoshin, Nikolay Solodovchenko, Mingzhao Song, Yong Li, Mihail Petrov, Andrey Bogdanov